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/*

 * Copyright (c) 2002-2005 The TenDRA Project <http://www.tendra.org/>.

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions are met:

 *

 * 1. Redistributions of source code must retain the above copyright notice,

 *    this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright notice,

 *    this list of conditions and the following disclaimer in the documentation

 *    and/or other materials provided with the distribution.

 * 3. Neither the name of The TenDRA Project nor the names of its contributors

 *    may be used to endorse or promote products derived from this software

 *    without specific, prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS

 * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,

 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR

 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,

 * EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,

 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;

 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,

 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR

 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF

 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 *

 * $Id$

 */

/*

    		 Crown Copyright (c) 1997

    This TenDRA(r) Computer Program is subject to Copyright

    owned by the United Kingdom Secretary of State for Defence

    acting through the Defence Evaluation and Research Agency

    (DERA).  It is made available to Recipients with a

    royalty-free licence for its use, reproduction, transfer

    to other parties and amendment for any purpose not excluding

    product development provided that any such use et cetera

    shall be deemed to be acceptance of the following conditions:-

        (1) Its Recipients shall ensure that this Notice is

        reproduced upon any copies or amended versions of it;

        (2) Any amended version of it shall be clearly marked to

        show both the nature of and the organisation responsible

        for the relevant amendment or amendments;

        (3) Its onward transfer from a recipient to another

        party shall be deemed to be that party's acceptance of

        these conditions;

        (4) DERA gives no warranty or assurance as to its

        quality or suitability for any purpose and DERA accepts

        no liability whatsoever in relation to any use to which

        it may be put.

*/

#include "config.h"

#include "file.h"

#include "types.h"

#include "fetch.h"

#include "utility.h"

/*

    CURRENT FILE POINTER

    As they are read from the input file bits are stored in input_buff.

    The current number of bits in the buffer is bits_in_buff.  bytes_read

    records the position in the input file.

*/

unsigned bits_in_buff = 0;

long bytes_read = 0;

static unsigned long input_buff = 0;

/*

    ALIGN TO NEXT BYTE BOUNDARY

    Any bits remaining in the current byte are ignored.

*/

void

byte_align(void)

{

    bits_in_buff = 0;

    return;

}

/*

    FETCH A NUMBER OF BITS

    This routine reads the next n bits from the input file and returns

    them as a long.

*/

long

fetch(int n)

{

    unsigned long s;

    unsigned long r = 0;

    unsigned b = (unsigned)n;

    while (b) {

	unsigned m;

	if (bits_in_buff == 0) {

	    int c = getc(input);

	    bytes_read++;

	    if (c == EOF) {

		input_error("Premature end of file");

		c = 0xff;

	    }

	    bits_in_buff = BYTESIZE;

	    input_buff = (unsigned long)(c & 0xff);

	}

	m = (b <= bits_in_buff ? b : bits_in_buff);

	s = (input_buff << m);

	r = ((r << m) | ((s >> BYTESIZE) & 0xff));

	b -= m;

	bits_in_buff -= m;

	input_buff = (s & 0xff);

    }

    return((long)r);

}

/*

    FIND CURRENT POSITION IN FILE

    The current position in the input file (in bits) is returned.

*/

long

input_posn(void)

{

    return(BYTESIZE * bytes_read - (long)bits_in_buff);

}

/*

    GO TO A POSITION IN FILE

    The position in the input file is set to the nth bit.

*/

void

input_goto(long n)

{

    int b = (int)(n % BYTESIZE);

    bytes_read = (n / BYTESIZE);

    bits_in_buff = 0;

    if (fseek(input, bytes_read, SEEK_SET)) {

	bits_in_buff = (unsigned)b;

	input_error("Illegal seek command");

	return;

    }

    if (b)IGNORE fetch(b);

    return;

}

/*

    SKIP A NUMBER OF BITS

    The next n bits in the input file are ignored.

*/

void

input_skip(long n)

{

    if (n <= 4 * BYTESIZE) {

	IGNORE fetch((int)n);

    } else {

	long m = input_posn() + n;

	input_goto(m);

    }

    return;

}